1. Field of the Invention
The present invention relates in general to a low dielectric constant plasma polymerized thin film and a manufacturing method thereof, and more particularly, to a plasma polymerized thin film for use in semiconductor devices, which has a low dielectric constant and is also improved in terms of mechanical properties including hardness and elastic modulus, and to a method of manufacturing the same.
2. Description of the Related Art
Presently, one of the chief steps in the fabrication of a semiconductor apparatus is the formation of metal and dielectric thin films on a substrate through the chemical reaction of gases. This deposition process is referred to as chemical vapor deposition (CVD). Typically, in a thermal CVD process, reactant gases are supplied to the surface of a substrate, so that a thermally-induced chemical reaction occurs on the surface of the substrate, thus forming a thin film of a predetermined thickness. Such a thermal CVD process is conducted at high temperatures, which may thus damage device geometries in which layers are formed on the substrate. A preferred example of a method of depositing metal and dielectric thin films at relatively low temperatures includes plasma-enhanced CVD (PECVD) disclosed in U.S. Pat. No. 5,362,526, entitled “Plasma-enhanced CVD process using TEOS for depositing silicon oxide”, which is hereby incorporated by reference into this application.
According to PECVD, radio frequency (RF) energy is applied to a reaction zone, thus promoting the excitation and/or dissociation of reactant gases, thereby creating plasma of highly reactive species. High reactivity of the released species reduces the energy required for a chemical reaction to take place and thus lowers the required temperature for such PECVD. Thus, semiconductor device geometries have dramatically decreased in size due to the introduction of such an apparatus and method.
Further, in order to decrease the RC delay of the multilayered metal film used for integrated circuits of a ULSI semiconductor device, thorough research into preparation of interlayer insulating films used for metal wires using material having a low dielectric constant (k≦2.4) is being conducted these days. Such a low dielectric constant thin film is formed of an organic material or an inorganic material such as a fluorine (F)-doped oxide film (SiO2) and a fluorine-doped amorphous carbon film (a-C:F). Polymerized thin films having a relatively low dielectric constant and relatively superior thermal stability are used mainly as an organic material.
Very useful to date are interlayer insulating films of silicon dioxide (SiO2) or silicon oxyfluoride (SiOF), which have some defects, such as high capacitance and long RC delay time, upon fabrication of ultra-highly integrated circuits of 0.5 μm or less, and thus intensive research into substituting for it a novel low dielectric constant material is being conducted recently, but satisfactory solutions have not yet been proposed.
Examples of the low dielectric constant material presently usable instead of SiO2 include organic polymers for spin coating, such as BCB (benzocyclobutene), SILK (available from DOW Chemical), FLARE (fluorinated poly(arylene ether), available from AlliedSignal, now Honeywell International), and polyimide, materials for CVD, such as Black Diamond (available from Applied Materials), Coral (available from Novellus), SiOF, alkyl silane, and parylene, and porous thin film materials, such as xerogel or aerogel.
Most polymerized thin films are formed through spin casting by which a polymer is chemically synthesized, applied on a substrate through spin coating, and then cured. The low dielectric constant thin film thus formed advantageously has a low dielectric constant because the pores having a size of single-digits of nanometers are formed in the thin film, thus lowering the density of the thin film. The organic polymers which are typically deposited through spin coating have a low dielectric constant and superior planarization, but have poor thermal stability due to low heat-resistant threshold temperatures below 450° C. and are thus inadequate in terms of availability. Further, the above organic polymers are disadvantageous because the pores are non-uniformly distributed in the film owing to a large size thereof, thus causing many problems upon the manufacture of devices. Furthermore, the above organic polymers are problematic in that they come into poor contact with upper and lower wiring materials, that thin films resulting therefrom intrinsically incur high stress upon thermal curing, and also that the dielectric constant thereof varies attributable to water absorption, undesirably decreasing the reliability of the device.